Using matt laquer on canopies, clear parts.

Laquer especially will attack bare plastic. Never apply this to unpainted plastic, particualrly clear parts. Further, you want glazing to remain glossy.

Any flat clearcoat, whether it be lacquer, enamel or acrylic, will fog clear parts. Regardless of the solvent action to which Al is referring, clear flat coats contain a "matting agent", typically fine-ground silica, which is not completely transparent. Always leave your clear parts masked until after the final flat coat is applied.